Thermoelectric materials and devices may be utilized to obtain electrical energy from a thermal gradient. Current thermoelectric materials have a limited thermoelectric conversion efficiency which may be defined in terms of the formulaZT=S2γ/κ×T. The ZT of the above formula or figure of merit is related to the macroscopic transport parameters of the material including the Seebeck coefficient S, the electrical conductivity γ and the thermal conductivity κ.
In order to improve the thermoelectric conversion efficiency one may increase the Seebeck coefficient and electrical conductivity while lowering the thermal conductivity. Increasing the ZT is difficult as the three parameters S, γ and κ are interrelated. For example, doping of a specific material may increase the electrical conductivity while decreasing the Seebeck coefficient and increasing the thermal conductivity. There is therefore a need in the art for a material having a ZT improved over conventional materials. There is also a need in the art for increasing the thermoelectric conversion by increasing or maintaining the Seebeck coefficient and electrical conductivity while lowering a thermal conductivity.
Nanostructured materials may be utilized to produce thermoelectric nanoparticles and materials for a thermoelectric composite materials. However, such nanostructured materials may be difficult and expensive to manufacture and may be difficult to process to form a composite material. Conventional thermoelectric nanostructured materials and processes for producing the same are unable to provide enhanced thermoelectric conversion efficiency. Additionally, conventional processes for producing thermoelectric nanoparticles are not cost efficient, or scalable, and do not produce thermoelectric composites having improved properties that overcome the technical problems associated with conventional thermoelectric nanoparticles and thermoelectric composite materials.
The semiconductor materials that are used to make thermoelectric materials are often classified as N-type or P-type. An N-type semiconductor material has an excess of negative electron charge carriers and thereby provides greater electron conduction than the native semiconductor material. In contrast a P-type semiconductor has an excess of positive charge carriers (e.g., holes).
Conventionally the native semiconductor material is doped with a dopant or mixed with a further element to obtain N-type or P-type behavior. Elements and dopants for semiconductor materials such as bismuth telluride include selenium (N-type) and antimony (P-type). Bismuth selenium telluride is an example of a ternary material that exhibits N-type behavior due to the inclusion of atoms of selenium in the bismuth tellurium matrix structure.